1. Field of the Invention:
The present invention relates to a moldable polyamide resin composition. The advantages of the composition are that, while dwelling in mold cylinders, it retains good fluidity, that the amount of cushion resin needed for molding the composition fluctuates little, and that occurrence of failure such as cobwebbing in molding the composition is reduced; and the advantages of the moldings of the composition are that they have good impact resistance and good appearance.
2. Description of Related Art:
As having good mechanical properties, good abrasion resistance, good electric properties, good chemical resistance and good workability, polyamide resins such as typically nylon 6 and nylon 66 are widely used as engineering plastics in various fields, for example, in the field of automobiles, in the field of electric and electronic appliances and in other fields of building materials, sundries, etc.
High-quality plastics of many applications are being much needed in those fields, and improving the quality of plastics is therefore much desired. For example, in the field of automobiles, it is desired to reduce as much as possible the destruction of the environment owing to exhaust gas. For this, automobile parts are being small-sized and thin-walled so as to produce lightweight and compact cars. On the other hand, in the field of electric and electronic appliances, portable personal computers are being popularized, and housings for them are desired to be lightweight. At present, polyamide resins are used for the applications in those fields, and it is desired to further reduce the wall thickness of the moldings of polyamide resins. For this, the fluidity of polyamide resins must be improved.
In that situation, a large number of polymers having various novel characteristics have been developed and put on the market. Of those, optically-anisotropic, liquid-crystalline polymers characterized by the parallel orientation of molecular chains are specifically noticed, as having high fluidity and good mechanical properties. In particular, as the polymers of those types have especially high strength and stiffness, there is much increasing great demand for small-sized moldings of the polymers in the field of electrical engineering and electronics and also in the field of office appliances. Various techniques of mixing two different resins, liquid-crystalline resin and thermoplastic resin, have heretofore been proposed so as to obtain resin mixtures having good characteristics of the two resins, for example, as in JP-A 56-115357, 1-259062, 3-54222, 5-86286, 9-12875, etc.
However, merely mixing the two polymers could not produce significant improvements in the physical properties of the resulting mixture, since the two polymers do not have good compatibility with each other. Because of their poor compatibility, either one of the two polymers a foreign impurity component in the mixture of the two, whereby the impact strength of the moldings of the mixture is lowered. In addition, it has been found that, when the mixture is molded in a large-sized molding machine, it often undergoes amide-ester interaction owing to long residence time in the mold. As a result, the fluidity of the mixture in the mold is rather lowered, contrary to the intended object of increasing the fluidity of resin mixtures. JP-A-9-12875 discloses a resin composition comprising a specific, terminal-blocked polyamide and a liquid-crystalline resin. In this, they say that monocarboxylic acids and acid anhydrides are usable as the terminal-blocking agent for the polyamide. Specifically, the invention disclosed is to blend a polyamide and a liquid-crystalline resin in a simple ordinary mixing manner, in which the polyamide is terminal-blocked during its polymerization so as to retard the interaction with the liquid-crystalline resin in the resulting mixture. In the disclosed method, however, the compatibility of the two polymers is still poor, and the physical properties of the resulting mixture of the two polymers are inevitably degraded. We, the present inventors tried the method, using a large-sized molding machine for producing large-sized moldings, and, as a result, have found that, since the resin mixture inevitably dwells in the cylinder, it decomposes or foams and even its viscosity increases. In our experiment, therefore, the fluidity of the resin mixture rather lowered. It is believed that the phenomenon of the viscosity increase to lower the fluidity of the resin mixture was caused by amide-ester interaction having occurred between the two resins in the mixture.